On a problem in eigenvalue perturbation theory

We consider additive perturbations of the type $K_t=K_0+tW$, $t\in [0,1]$, where $K_0$ and $W$ are self-adjoint operators in a separable Hilbert space $\mathcal{H}$ and $W$ is bounded. In addition, we assume that the range of $W$ is a generating (i.e., cyclic) subspace for $K_0$. If $\lambda_0$ is an eigenvalue of $K_0$, then under the additional assumption that $W$ is nonnegative, the Lebesgue measure of the set of all $t\in [0,1]$ for which $\lambda_0$ is an eigenvalue of $K_t$ is known to be zero. We recall this result with its proof and show by explicit counterexample that the nonnegativity assumption $W\geq 0$ cannot be removed.Comment: 10 pages; added Lemma 2.4, typos removed; to appear in J. Math. Anal. App

A competitive environment for exploratory query expansion

Most information workers query digital libraries many times a day. Yet people have little opportunity to hone their skills in a controlled environment, or compare their performance with others in an objective way. Conversely, although search engine logs record how users evolve queries, they lack crucial information about the user's intent. This paper describes an environment for exploratory query expansion that pits users against each other and lets them compete, and practice, in their own time and on their own workstation. The system captures query evolution behavior on predetermined information-seeking tasks. It is publicly available, and the code is open source so that others can set up their own competitive environments

Extracting corpus specific knowledge bases from Wikipedia

Thesauri are useful knowledge structures for assisting information retrieval. Yet their production is labor-intensive, and few domains have comprehensive thesauri that cover domain-specific concepts and contemporary usage. One approach, which has been attempted without much success for decades, is to seek statistical natural language processing algorithms that work on free text. Instead, we propose to replace costly professional indexers with thousands of dedicated amateur volunteers--namely, those that are producing Wikipedia. This vast, open encyclopedia represents a rich tapestry of topics and semantics and a huge investment of human effort and judgment. We show how this can be directly exploited to provide WikiSauri: manually-defined yet inexpensive thesaurus structures that are specifically tailored to expose the topics, terminology and semantics of individual document collections. We also offer concrete evidence of the effectiveness of WikiSauri for assisting information retrieval

What Are The Best Guidelines. For Dredging And Placement Of Dredged Materials?

During the~ next 25 years, more than 280 millicm cubic yards of sediment will be dredged from the Chesapeake Bay and its tributaries (Table 1). Altogether more than 800 million dollars will be spent to deepen ports and maintain shipping channels. About one-third of the maintenance dredgin~; will be done in ports and harbors where the sediment is contaminated by industrial wastes and sewage discharge. Because of long-continued disposal of dredged material, the region is losing its physical capacity to assimilate more material. Where then can these enormous loads be placed at acceptable costs? And what are the best guidelines for selecting placement sites to accomodate polluted material? What guidelines are needed for predicting the short and long-term impacts of dredging and disposal? These are! important management questions facing bay scientists, engineers, and managers who aim to protect priority resources and at the same time to accomodate shipping that requires deeper channels and efficient navigation.https://scholarworks.wm.edu/vimsbooks/1173/thumbnail.jp

New and improved demonstrations for use in teaching scientific principles in chemistry

Thesis (Ed.M.)--Boston Universit